\documentclass[a4paper,dvipdfm]{slides}
\usepackage{graphicx}

\begin{document}
\begin{center}

\includegraphics[scale=1.5]{usb485_brd_bvalues.pdf}
\includegraphics[scale=1.5]{usb485_brd_tvalues.pdf}

\end{center}
\end{document}
